U.S. patent application number 10/849174 was filed with the patent office on 2004-12-02 for electric current control method and apparatus for use in gas generators.
This patent application is currently assigned to Toyo Tanso Co., Ltd.. Invention is credited to Hiraiwa, Jiro, Tojo, Tetsuro, Yoshimoto, Osamu.
Application Number | 20040238374 10/849174 |
Document ID | / |
Family ID | 33128235 |
Filed Date | 2004-12-02 |
United States Patent
Application |
20040238374 |
Kind Code |
A1 |
Tojo, Tetsuro ; et
al. |
December 2, 2004 |
Electric current control method and apparatus for use in gas
generators
Abstract
The invention provides a method and apparatus for current
control in gas generators capable of generating a fluorine or
fluoride gas by and in which the electrolysis can be maintained in
an optimum condition, stable operation is possible and no manpower
is demanded. According to the method of current control in gas
generators for generating a fluorine or fluoride gas by
electrolysis of an electrolytic bath 5 comprising a hydrogen
fluoride-containing mixed molten salt using a carbon electrode as
the anode 4a, the range of voltage fluctuation between the cathode
4b and anode 4a as occurring when a certain current is applied to
the gas generator is measured, and current application is continued
while varying the current amount to be applied according to the
voltage fluctuation range.
Inventors: |
Tojo, Tetsuro; (Osaka-shi,
JP) ; Hiraiwa, Jiro; (Osaka-shi, JP) ;
Yoshimoto, Osamu; (Osaka-shi, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
Toyo Tanso Co., Ltd.
Osaka-shi
JP
|
Family ID: |
33128235 |
Appl. No.: |
10/849174 |
Filed: |
May 20, 2004 |
Current U.S.
Class: |
205/619 ;
204/228.1; 204/230.2; 205/359; 205/411 |
Current CPC
Class: |
C25B 1/245 20130101;
C25B 15/02 20130101 |
Class at
Publication: |
205/619 ;
205/359; 205/411; 204/228.1; 204/230.2 |
International
Class: |
B23H 003/02; C25D
017/00; C25B 009/04; C25C 003/20; C25B 015/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 28, 2003 |
JP |
2003-150474 |
Claims
What is claimed is:
1. A method of current control in a gas generator generating a
fluorine or fluoride gas by electrolysis of an electrolytic bath
comprising a hydrogen fluoride-containing mixed molten salt using a
carbon electrode as the anode which method comprises measuring the
range of voltage fluctuation between the cathode and anode when a
certain constant current is applied to the gas generator and
carrying out current application while varying the current amount
to be applied according to the voltage fluctuation range.
2. A method of current control in a gas generator generating a
fluorine or fluoride gas by electrolysis of an electrolytic bath
comprising a hydrogen fluoride-containing mixed molten salt using a
carbon electrode as the anode which method comprises measuring the
range of voltage fluctuation between the cathode and anode when a
certain constant current is applied to the gas generator and
carrying out current application until arrival at a target
operation current level while varying the current amount to be
applied according to the voltage fluctuation range.
3. A method of current control in a gas generator generating a
fluorine or fluoride gas as set forth in claim 1 or 2, wherein the
range of voltage fluctuation between the anode and cathode is
measured and the current amount to be applied is varied according
to the voltage fluctuation range to thereby continue the
electrolysis further after arrival of the current application at
the target operation current level.
4. A method of current control in a gas generator generating a
fluorine or fluoride gas as set forth in claim 2 or 3, wherein
current application is carried out until a predetermined value
level while repeatedly increasing, decreasing or maintaining the
current to be applied.
5. A method of current control in a gas generator generating a
fluorine or fluoride gas as set forth in any of claims 1 to 4,
wherein the current to be applied at a time is not more than 5
A/dm.sup.2 relative to the effective electrolysis surface area on
the anode.
6. A method of current control in a gas generator generating a
fluorine or fluoride gas as set forth in any of claims 1 to 5,
wherein the gas generator has a plurality of independent power
sources.
7. An apparatus for current control in a gas generator generating a
fluorine or fluoride gas which comprises a carbon electrode for
electrolyzing an electrolytic bath comprising a hydrogen
fluoride-containing mixed molten salt, a constant current supply
source for current application between the anode and cathode,
current control means connected with the constant current supply
source and serving to control the current applied, first measuring
means for measuring the time from the start of electrolytic current
application, voltage measuring means for measuring the fluctuation
in the voltage between the anode and cathode after the lapse of a
predetermined period of time as measured by the first measuring
means, second measuring means for measuring the period of time of
the voltage fluctuation range measurement, and current determining
means for determining the current to be applied next based on the
range of voltage fluctuation between the anode and cathode.
8. An apparatus for current control in a gas generator generating a
fluorine or fluoride gas as set forth in claim 7, wherein the
constant current supply source comprises a plurality of constant
current supply sources.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to a method and an apparatus for
electric current control in gas generators which generate a
fluorine or fluoride gas.
[0003] 2. Description of the Related Art
[0004] Conventionally, fluorine is produced by electrolysis of a
molten salt containing a fluoride such as HF, as shown in the
equation (1):
F.sup.-.fwdarw.1/2F.sub.2+e.sup.- (1) (fluorine generation
reaction).
[0005] On that occasion, hydrogen is generated from the cathode, as
shown by the equation (2):
2H.sup.++2e.sup.-.fwdarw.H.sub.2 (2) (hydrogen generation
reaction).
[0006] However, among the reactions shown above by the equations
(1) and (2), the fluorine generation reaction, which occurs on the
anode, is accompanied by very complicated side reactions, as shown
by the equations (3) to (10):
xC+F.sup.-.fwdarw.(C.sub.x.sup.+F.sup.-)+e.sup.- (3)
(fluorine-carbon intercalation compound formation reaction)
[0007] The reaction shown by the equation (3) is a reaction
proceeding within electrode carbon crystals, by which reaction the
surface energy of the crystals increases and the wetting thereof
with the electrolytic bath is improved and, further, the
conductivity thereof as the electrode is improved as a result of
hole conduction caused by hole creation within the crystals by
drawing of .pi. electron on carbon atom toward fluorine atoms.
C+2F.sub.2.fwdarw.CF.sub.4 (4) (carbon tetrafluoride formation
reaction)
[0008] The reaction represented by the equation (4) indicates that
the fluorine gas generated by electrolysis reacts with carbon atoms
electrode surface to generate the carbon tetrafluoride gas. This
gas, when it enters a fluorine-containing gas, in particular the
fluorine gas, becomes an impurity and reduces the purity of the
fluorine gas. This gas is close in such properties as boiling point
to the fluorine gas and therefore is difficult to eliminate from
the fluorine gas. Thus, the use of a carbon anode hardly allowing
this reaction to occur is preferred from the high purity gas
generation viewpoint.
2H.sub.2O.fwdarw.O.sub.2+4H.sup.++4e.sup.- (5) (oxygen generation
reaction)
xC+1/2O.sub.2.fwdarw.C.sub.xO (6) (graphite oxide formation
reaction)
2xC+yF.sub.2.fwdarw.(CF).sub.x (7) (graphite fluoride generation
reaction)
[0009] The equations (5) to (7) indicate a series of reactions.
When water, which is lower in discharge potential than HF, is
present in the electrolytic bath, water is electrolyzed according
to the equation (5) before HF. The oxygen generated by this
electrolytic reaction reacts with the electrode carbon to form
graphite oxide according to the equation (6). This compound is
unstable and the fluorine generated according to the equation (1)
readily substitutes for the oxygen of this compound to generate
graphite fluoride, as shown by the equation (7).
[0010] Graphite fluoride is very low in surface energy and, when
graphite fluoride is formed on the electrode surface, that portion
cannot come into contact with the electrolytic bath, causing
polarization, which inhibits the progress of the electrolytic
reaction. When the coverage of graphite fluoride, which is very low
in surface energy, as mentioned above, exceeds 20% relative to the
electrode surface area, the electrode surface will not be wetted
with the electrolytic bath at all but the so-called "anode effect"
condition will result. More specifically, the electrode cannot come
into contact with the electrolytic bath, so that the resistance of
the electrode surface becomes infinite and the path of the
electrolytic current is thus barred, with the result that the
electrolytic potential rapidly increases and a state arises in
which electrolysis is no more possible at all.
[0011] This reaction tends to occur when the water content is high
in the electrolytic bath, for example just after preparation of the
electrolytic bath or just after starting of feeding of hydrogen
fluoride as the raw material. When the increase in the current to
be applied to the effective electrode surface area is excessive in
electrolytic current application, too, these reactions tend to
occur.
[0012] As the HF in the electrolytic bath is consumed, the HF
concentration in the electrolytic bath comprising KF.multidot.xHF
lowers and, when x becomes lower than 1.8, the ice point rises to
100.degree. C. or above and the electrolytic bath precipitates out
on the anode and cathode, respectively, at a controlled temperature
of 90.degree. C. to 100.degree. C. under the operation conditions
of the electrolyzer; in many cases, it precipitates out on the
cathode (cylinder or nickel) rather than on the anode where
graphite fluoride is formed according to the equation (7). When
this phenomenon occurs, the bath voltage increases due to an
increase in cathode resistance. This increase in bath voltage is a
problem that can be solved by adjusting the HF concentration in the
electrolytic bath to a predetermined level. However, once the
melting point of the bath has risen and solidification has
occurred, it is difficult to melt again the bath that has
solidified in the electrolyzer. Therefore, once such a phenomenon
has occurred, a much longer time is required for adjusting the HF
concentration in a solidified portion as compared with HF
concentration adjustment in the ordinary electrolytic bath that is
in a molten state.
Fe.sup.2+.fwdarw.+Fe.sup.3++e.sup.- (8) (oxidation reaction of iron
ions eluted)
Ni.sup.2+.fwdarw.+Ni.sup.4++2e.sup.- (9) (oxidation reaction of
nickel ions eluted)
[0013] As shown by the equations (8) and (9), the iron and/or
nickel ions electrochemically eluted from the structural materials
of the electrolyzer are further oxidized on the anode to give
Fe.sup.3+ or Ni.sup.4+. If the fluorides of these ions are present
in the bath, they form complexes with KF. These complexes adhere to
the anode in the manner of electrophoresis during electrolysis.
These insulating deposits cause polarization on the anode. The
phenomenon occurring during operation includes fluctuations and/or
a slow rise in bath voltage. Further, when the contents of these
impurities in the electrolytic bath increase, the viscosity of the
electrolytic bath increases and splash entrainment tends to occur
readily. When splash entrainment occurs, the electrolytic bath
composition fluctuates with the lapse of time, possibly causing
choking in piping portions and/or causing fluctuations in pressure
in the electrolyzer.
1/2F.sub.2+1/2H.sub.2.fwdarw.HF (10) (reduction reaction of H.sub.2
and F.sub.2)
[0014] The reaction according to the equation (10) occurs when
fluorine gas and hydrogen gas mix with each other. When this
reaction occurs in the electrolytic bath, raw material recovery
results, and the current efficiency in the fluorine generation
reaction lowers. In any case, this is a reaction unfavorable for
the maintenance of the main reaction in the electrolysis.
[0015] The reactions according to the above equations (1) to (10)
except for the equation (2) occur on the anode. On the anode
surface where such competitive reactions proceed, the surface
conditions, inclusive of gas desorption and adsorption, are always
changing, and this results in fluctuations in bath voltage relative
to the current applied. Under such circumstances, a method of
current application as resulting from due consideration of these
reactions should be carried out so that fluorine may be generated
smoothly with a current efficiency of 95% or higher even when use
is made of a bath conditioned to sufficiently remove H.sub.2O in
the bath.
[0016] In the case of industrial electrolyzers in ordinary use, the
operation conditions are manually controlled, and watchmen adjust
the operation conditions after observation by them of some or other
noticeable abnormality, such as an abnormality in electrolytic
voltage. Thus, they can operate only allopathically. Under the
existing circumstances, when the electrolysis condition is found
worsened, they lower the output repeatedly and, finally, they stop
the electrolysis for repairing. At the time of stopping the
electrolysis, the electrode is also found damaged in many
instances, hence electrode replacement becomes essential. When, on
that occasion, the suspension period and the manpower required for
repairing and other factors are taken into consideration, this
repair work costs very much. Considering these together, it is
necessary to always monitor the electrolyzer condition
automatically by means of a control system, not by watchmen, so
that the electrolyzer may be operated stably while preventing any
factors from inhibiting the electrolysis in accordance with the
electrolyzer condition.
[0017] Under such circumstances, automatic operation has been
attempted, for example, by on/off operations, depending on the bath
liquid level, of the current supply means placed under the control
of signals from a bath liquid level sensor provided within the
electrolyzer so that the electrolysis conditions may be controlled
and the liquid level may be maintained at a constant level (cf.
e.g. JP Kohyo H09-505853).
[0018] However, as for the method described in the above-cited
patent document, the current situation is that operators on site
monitor the state of electrolysis and control the electrolysis
conditions according to changes therein until it becomes possible
to effect stable gas generation.
[0019] It is an object of the present invention, which has been
made in view of the problems discussed above, to provide a method
and an apparatus for current control in gas generators capable of
generating a fluorine or fluoride gas by which method and apparatus
the electrolysis can be maintained in an optimum state and stable
operation is made possible without requiring manpower.
SUMMARY OF THE INVENTION
[0020] The present inventors made intensive investigations in an
attempt to solve the above problems and, as a result, found a
method of operating the electrolyzer always stably by measuring the
electrolytic voltage between the anode and cathode during
electrolysis, precisely monitoring the voltage fluctuation range,
thereby estimating the state within the electrolyzer, minutely
determining the electrolysis conditions based on that estimation,
and realizing them. They further developed a control apparatus in
which the above method is employed and which can monitor the state
of the electrolyzer always automatically without manpower and can
prevent electrolysis-inhibiting factors to thereby enable stable
operation. Thus, they have completed the present invention.
[0021] In an aspect, the method of current control in gas
generators generating a fluorine or fluoride gas according to the
invention is a method of current control in a gas generator
generating a fluorine or fluoride gas by electrolysis of an
electrolytic bath comprising a hydrogen fluoride-containing mixed
molten salt using a carbon electrode as the anode and is
characterized in that the range of voltage fluctuation between the
cathode and anode when a certain current is applied to the gas
generator and current application is carried out while varying the
level thereof according to the voltage fluctuation range.
[0022] When, in carrying out electrolysis in the gas generator
generating a fluorine or fluoride gas, a constant current is
applied between the anode and cathode, the range of electrolytic
voltage fluctuation between the anode and cathode, which is one of
the electrolysis conditions, is measured. When the fluctuation
range is narrow, it can be confirmed that the electrolytic state is
normal; hence, a certain current can be further applied. In case of
an abnormality during electrolysis, the abnormality manifests
itself mostly as an increase in the electrolytic voltage
fluctuation range. In that case, this is recognized as the
occurrence of an abnormality in the gas generator and further
current supply is once suspended according to the largeness of the
electrolytic voltage fluctuation range for confirmation of the
actual state, or it is possible to reduce the certain current as
compared with that applied so far and confirm whether an
abnormality still occurs in that state.
[0023] In another aspect, the method of current control in gas
generators generating a fluorine or fluoride gas according to the
invention is a method of current control in a gas generator
generating a fluorine or fluoride gas by electrolysis of an
electrolytic bath comprising a hydrogen fluoride-containing mixed
molten salt using a carbon electrode as the anode and is
characterized in that the range of voltage fluctuation between the
cathode and anode when a certain current is applied to the gas
generator is measured and current application is carried out to
attain a target operation current level while varying the level
thereof according to the voltage fluctuation range.
[0024] By repeating the operation of applying a constant current
while repeating the above method of the invention, it becomes
possible to increase the current to be applied until a final target
operation current level while repeatedly confirming that there is
no abnormality in electrolysis condition. As a result, a fluorine
or fluoride gas can be generated very safely. The term "target
operation current level" as used herein means a necessary and
sufficient current value to be applied between the anode and
cathode for generating a required gas amount within the range up to
a maximum current capacity applicable between the anode and cathode
by the electrolytic power source of the generator.
[0025] In a further aspect, the method of current control in gas
generators generating a fluorine or fluoride gas according to the
invention comprises measuring the range of voltage fluctuation
between the anode and cathode and varying the current to be applied
according to the voltage fluctuation range to thereby continue the
electrolysis further after arrival of the current application at
the target operation current level.
[0026] Thus, in the above-mentioned case of abnormality occurrence
during electrolysis, the abnormality manifests itself mostly as an
increase or decrease in the range of voltage fluctuation between
the anode and cathode. In that case, it is recognized that there is
an abnormality in the gas generator; and the current level is
reduced as compared with the operation current. On that occasion,
the method of current control in gas generators comprises repeating
the same operation as in the second aspect and carrying out current
application again until the target operation current level is
arrived at. In continuing steady electrolysis for continuous gas
generation after current application to the target operation
current level, that the electrolysis state is normal can be
confirmed by measuring the range of voltage fluctuation between the
anode and cathode and confirming that the fluctuation range is
within a predetermined range of voltage fluctuation; the operation
current can then be continuously applied.
[0027] In a further aspect, the method of current control in gas
generators generating a fluorine or fluoride gas according to the
invention comprises carrying out current application until a
predetermined value level while repeatedly increasing, decreasing
or maintaining the current to be applied.
[0028] Thus, in the case of abnormality occurrence during
electrolysis, the abnormality manifests itself mostly as an
increase or decrease in the range of voltage fluctuation between
the anode and cathode. In that case, it is recognized that there is
an abnormality in the gas generator; the method of current control
in gas generators thus comprises either suspending further current
application for confirming the actual state, or decreasing the
current as compared with the level applied previously to confirm
whether there is still an abnormality in that state. Therefore,
even when a current level lower than the operation current is
selected and current application is carried out until that selected
value, the range of voltage fluctuation between the anode and
cathode is measured and, when the fluctuation range is within a
predetermined voltage fluctuation range, it can be confirmed that
the state of electrolysis is normal, hence further certain current
application is possible.
[0029] In a further aspect of the method of current control in gas
generators generating a fluorine or fluoride gas according to the
invention, the current to be applied at a time is not more than 5
A/dm.sup.2 relative to the effective electrolysis surface area on
the anode.
[0030] If an excessive current is applied at a time because of
hastened production on the production site in a gas generator
generating a fluorine or fluoride gas, the rate of formation of
(CF).sub.n, which causes polarization, according to the equation
(7) among the reactions indicated by the equations (4) to (10)
increases, hence polarization will be caused. In case of occurrence
of this abnormality, it is difficult to detect the electrolytic
voltage fluctuation based on an abnormality due to a worsened
electrode condition since the change due to current application is
too rapid even when the electrolytic voltage between the anode and
cathode is being measured. Even if this abnormality can be
detected, the symptoms are already in a worst condition, so that it
is difficult to avoid or eliminate the abnormal state or bring
about a recovery from that state by reducing the current, for
instance. If the current to be applied at a time is excessively
small, a very long period of time is required to attain the target
operation current level and may cause a delay in required gas
supply. Therefore, the current to be applied at a time should be
not more than 5 A/dm.sup.2, preferably within the range of 1 to 3
A/dm.sup.2, relative to the effective electrolytic surface area on
the anode, whereby any delay in detection or worsening in condition
can be prevented.
[0031] In a further aspect of the method of current control in gas
generators generating a fluorine or fluoride gas according to the
invention, there are provided a plurality of independent power
sources.
[0032] In large gas generators for generating a fluorine or
fluoride gas whose current capacity is 1,000 A to 5,000 A, for
instance, the electrodes generally comprise 10 to 32 plates. As for
the method of electrode mounting, one to ten plates are fixed to
each of a plurality of current collectors. Therefore, in case of
the occurrence of an abnormality, the state thereof can be detected
by measuring the range of voltage fluctuation between the anode and
cathode. When, however, the electrode and/or electrolyzer will not
return to a normal state in spite of such operation as decreasing
the current application, the abnormality may generally have begun
from a part of the whole number of electrode plates. Therefore, by
employing a plurality of power sources and measuring the range of
electrolytic voltage fluctuation between the anode and cathode of
each current collector unit for each of the respective power
sources, it becomes possible to specify the site of abnormality
occurrence with ease. Once the abnormality site can be specified,
it becomes possible to operate the power source connected to the
abnormality site alone according to the degree of abnormality while
operating the other power sources under predetermined ordinary
conditions. Thus, by increasing the number of electrolytic power
sources but decreasing the capacity of each of the respective power
sources relative to the current capacity of the generator, it
becomes possible to finely control the generator depending on the
respective states of the plurality of electrodes.
[0033] The apparatus, or system, for current control in gas
generators generating a fluorine or fluoride gas according to the
invention comprises a carbon electrode for electrolyzing an
electrolytic bath comprising a hydrogen fluoride-containing mixed
molten salt, a constant current supply source for current
application between the anode and cathode, current control means
connected with the constant current supply source and serving to
control the current applied, first measuring means for measuring
the time from the start of electrolytic current application,
voltage measuring means for measuring the fluctuation in the
voltage between the anode and cathode after the lapse of a
predetermined period of time as measured by the first measuring
means, second measuring means for measuring the period of time of
the voltage fluctuation range measurement, and current determining
means for determining the current to be applied next based on the
range of voltage fluctuation between the anode and cathode.
[0034] When, in fluorine electrolysis, a certain current is applied
between the anode and cathode, the electrolytic voltage initially
fluctuates excessively even in a normal state of electrolysis and
then shows an almost constant value depending on the current
applied. Therefore, as shown in FIG. 3, the first measuring means
(timer 1) is used to measure a certain period of time during which
the range of electrolytic voltage fluctuation between the anode and
cathode should be neglected so that the initial excessive
fluctuation may not be detected as an abnormality (ST-3). This
time, when it is excessively long, will fail to detect
abnormalities and, when it is excessively short, the initial
voltage fluctuation range after the start of current application
will be detected as an abnormality. Therefore, a specific
measurement time can be selected within the range of 1 second to 5
minutes, preferably 6 seconds to 1 minute. After time measurement
by this first measuring means, the measurement of the range of
voltage fluctuation between the anode and cathode is started. The
period of time of this measurement is measured by the second
measuring means (timer 2). When it is too short, the change in
electrolytic voltage becomes relatively slow, hence cannot be
detected, rendering it difficult to succeed in abnormality
detection and, when it is too long, it may become too late to take
measures against the abnormality occurrence or an unnecessarily
long period may be required until the next application of a
constant current, hence the productivity may become poor.
Therefore, a specific measurement time should be selected within
the range of 1 second to 120 minutes, preferably 3 minutes to 30
minutes.
[0035] As for the range of electrolytic voltage fluctuation between
the anode and cathode, the voltage at the time of the start of the
voltage measurement period by the second measuring means is taken
as a "reference voltage" and the difference of the voltage at the
time of the end of the voltage measurement period from that
reference voltage is regarded as the range of electrolytic voltage
fluctuation. Based on the results of past studies of operation
conditions, the range of electrolytic voltage fluctuation between
the anode and cathode upon application of a constant current can be
divided into and judged as being in a normal range (ST-5), a
warning range (ST-6) and an abnormality range (ST-7). Although
these may vary depending on the shape of the electrolyzer and the
electrolysis controlling conditions, the range of "reference
voltage .+-.0 to 0.5 V", preferably the range of "reference voltage
.+-.0 to 0.3 V", may be regarded as the normal fluctuation range,
the value outside the normal range but in the range of "reference
voltage .+-.0.2 to 1.0 V", preferably "reference voltage .+-.0.3 to
0.5 V", may be regarded as belonging to the warning range, and the
"value outside the warning range" may be regarded as belonging to
the abnormality range. If these values are selected so that the
fluctuation range width may be too small, however, a fluctuation
within the normal range may be judged to be abnormal and the
operation may be disturbed thereby. If it is too great, the
occurrence of an abnormality may not be detected or it may become
difficult to improve the electrolysis state to return to
normalcy.
[0036] When the range of electrolytic voltage fluctuation as shown
in FIG. 2 is measured by the first measuring means, the second
measuring means and the means for measuring the electrolytic
voltage between the anode and cathode and found to be within the
normal range, a certain current is further applied (ST-2), the same
measurements are repeated and, finally, current application is
carried out until the operation current level intended of the power
source employed in the gas generator for generating a fluorine or
fluoride gas to thereby generate a required amount of a fluorine or
fluoride gas. If the range of electrolytic voltage fluctuation
between the anode and cathode is in the warning range, further
electrolytic current application (ST-6) is suspended, the
electrolytic voltage fluctuation range measurement is repeated by
the first measuring means, the second measuring means and the means
for measuring the electrolytic voltage between the anode and
cathode (ST-6, ST-7) and, when the fluctuation range can be judged
to be within the normal range based on the measurement results,
further electrolytic current application is restarted. If the range
of electrolytic voltage fluctuation is in the abnormality range
(ST-7), the constant electrolytic current applied previously is
reduced to the level before application, the electrolytic voltage
fluctuation range measurement is carried out using the first
measuring means, the second measuring means and the means for
measuring the electrolytic voltage between the anode and cathode
and, when the fluctuation can be judged to be within the normal
range based on the measurement results, electrolytic current
application is restarted. When the fluctuation is judged to be in
the warning range, the warning range procedure mentioned above is
followed. When an apparatus, or system, having all of these
functions is used, it is possible to select a target operation
current value and automatically apply an electric current in
constant amounts between the anode and cathode until the intended
current amount is reached and, after arrival at the intended
current amount, automatic operation is still possible by continuing
the current control in the same manner. It becomes also possible to
allow the electrolysis conditions to proceed always stably. In case
of abnormality occurrence during operation, the abnormality can be
detected early depending on the results of measurement of the range
of electrolytic voltage fluctuation between the anode and cathode
and the operation condition can be prevented from worsening by
adjusting the current amount.
[0037] In a further aspect of the apparatus for current control in
gas generators generating a fluorine or fluoride gas according to
the invention, there are provided a plurality of constant current
supply sources.
[0038] By employing a plurality of constant current supply sources
and measuring the range of electrolytic voltage fluctuation between
the anode and cathode of each current collector unit for the
respective power sources, it becomes easy to specify the site of
abnormality occurrence. Once the abnormality site can be specified,
it becomes possible to operate the power source connected to the
abnormality site alone according to the degree of abnormality while
operating the other power sources under predetermined ordinary
conditions. Thus, by increasing the number of electrolytic power
sources but decreasing the capacity of each of the respective power
sources relative to the current capacity of the generator, it
becomes possible to finely control the generator depending on the
respective states of the plurality of electrodes.
BRIEF DESCRIPTION OF THE DRAWINGS
[0039] FIG. 1 is a schematic representation of the main parts of an
embodiment of the gas generator according to the invention.
[0040] FIG. 2 is an illustration of the relationship between
applied current and voltage in the gas generator according to the
invention.
[0041] FIG. 3 is a flowchart illustrating the process for current
application to the electrodes.
[0042] FIG. 4 is an illustration of another embodiment of the gas
generator according to the invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0043] In the following, a mode of embodiment of the method of
current control in gas generators according to the invention is
described referring to the drawings. FIG. 1 is a schematic
representation of the gas generator according to the invention. As
shown in FIG. 1, the gas generator according to the invention
comprises, as main constituent elements thereof, a gas generator
portion 1 comprising a constant current supply source 3, and a
current control apparatus or system 2 connected to the constant
current supply source 3 and serving to control the current to be
applied to the electrodes 4.
[0044] The gas generator portion 1 comprises the constant current
supply source 3 connected to the electrodes 4 constituted of an
anode 4a, which is a carbon electrode, and a cathode 4b, and an
electrolytic cell or electrolyzer 6 in which an electrolytic bath 5
comprising a hydrogen fluoride-containing mixed molten salt, for
instance, is to be contained. The electrolyzer 6 is made of such a
metal as Ni, Monel, pure iron or stainless steel. The electrolyzer
6 is divided into an anode chamber 8 and a cathode chamber 9 by
means of a partition wall 7 made of Ni or Monel. Ni, among others,
is used as the cathode. The electrolyzer 6 is provided with
temperature adjusting means (not shown) for heating the
electrolyzer inside. The top cover 10 of the electrolyzer 6 is
provided with gas discharge ports for discharging gases generated,
upon electrolysis, from the anode and cathode, respectively.
[0045] The current control apparatus 2 is connected to the constant
current supply source 3 and is constituted of current control means
for controlling the current to be applied to a predetermined target
current amount, first measuring means for measuring a predetermined
period of time after application of a certain predetermined current
amount, voltage measuring means for measuring the range of voltage
fluctuation between the anode 4a and cathode 4b after the lapse of
that predetermined period of time, second measuring means for
measuring a predetermined voltage measurement time, and current
determining means for judging as to whether the range of voltage
fluctuation between the anode and cathode is normal or not and
determining, based on this judgment result, the amount of electric
current to be applied then.
[0046] Here, as regards the constant current supply source 3, it is
possible to supply the total current amount dividedly to respective
sets 4 of electrodes (anodes), including anodes 4a and cathodes 4b,
independently via the corresponding plurality of constant current
sources, as shown in FIG. 4. In this way, the current amounts
applied to the respective sets 4 of electrodes (anodes) can be
controlled separately. Even when any of the sets 4 of electrodes
(anodes) cannot be used due to some abnormality that has occurred
during electrolysis or other unexpected abnormality, the other
electrode sets 4 that are still usable can be used to continue
electrolysis; thus, even when there is some abnormality in the
electrolyzer, the electrolyzer can be operated stably while
minimizing the influence of the abnormality. Further, in coping
with the abnormality, it is only necessary to care for the
electrode set 4 in an abnormal condition alone and thereafter
restart the same. Thus, the electrode set 4 after abnormality
occurrence can be started under mild conditions while the normal
electrode sets 4 can be started relatively more quickly; in other
words, the former electrode set and the latter sets can be operated
under separate conditions, resulting in an improvement in
maintainability. It is of course possible to use only one power
source for a plurality of electrode sets 4.
[0047] The method of current control in the fluorine gas generator
constituted in the above manner is now described referring to FIG.
2 and FIG. 3.
[0048] First, a maximum current necessary for operation is
determined according to the capacity of the electrolyzer 6 (FIG. 3,
ST-1). Then, a certain constant current to be applied in each of a
plurality of steps is determined so that the maximum current may be
attained after the plurality of current application, and the
current for one step is applied (FIG. 3, ST-2). The current amount
to be applied in one step is selected at a level of not greater
than 5 A/dm.sup.2, preferably within the range of 1 to 3
A/dm.sup.2, relative to the anode surface area effective for
electrolysis. The current application is carried out in one or more
steps, preferably in three or more steps, until arrival at the
target maximum operation current. In this manner, even when a
carbon electrode is used as the anode 4a, the anode effect can be
inhibited from manifesting itself or, if the anode effect manifests
itself, the progress of that phenomenon can be suppressed by
selecting the current density at a lower level; thus, the
electrolyzer can be operated safely by controlling current
application or reducing the current amount at the time of judgment
to the effect that the range of electrolytic voltage fluctuation
between the anode and cathode is abnormal. When the certain
constant current is applied, the electrolytic voltage between the
anode and cathode onec rises and, after arrival at a peak, lowers
to a lesser extent as compared with the rise and then settles, as
shown in FIG. 2. Therefore, the timer 1, which is the first
measuring means, is operated so that the voltage fluctuation during
a period of 0.1 to 10 minutes just after current application
starting, during which the voltage fluctuation is great, may be
disregarded (FIG. 3, ST-3). After the lapse of the predetermined
period of time as set by the timer 1, the timer 2, which is the
second measuring means and monitors the range of voltage
fluctuation between the anode 4a and cathode 4b, operates (FIG. 3,
ST-4).
[0049] The voltage between the anode and cathode at the time of the
start of the voltage measurement period by the timer 2 is taken as
a "reference voltage", and the difference of the voltage at the
time of the ending of the period of voltage measurement by the
timer 2 from that reference voltage is regarded as the range of
electrolytic voltage fluctuation. The voltage fluctuation range is
judged as to whether it is in a normal range, namely the range of
"reference voltage .+-.0 to 0.5 V", preferably the range of
"reference voltage .+-.0 to 0.3 V" (FIG. 3, ST-5). If the voltage
fluctuation is within the normal range, the step ST-8 in FIG. 3 is
taken. The step ST-2 in FIG. 3 is again taken, and this step is
repeated until arrival at the predetermined upper limit current.
And, in the step ST-8 in FIG. 3, it is judged whether that current
is the predetermined target operation current or not. If it is the
target operation current, electrolysis is continued by maintaining
current application while monitoring the electrolytic voltage
fluctuation range (FIG. 3, ST-3). If it is not yet the target
operation current, the step ST-2 in FIG. 3 is again taken to return
to the next current application step (B in FIG. 2), the constant
current is further applied, and the step is repeated.
[0050] If, in the step ST-5 in FIG. 3, the voltage fluctuation is
outside the normal range, the step ST-5 in FIG. 3 is taken and
judgment is made as to whether the voltage fluctuation is in the
warning range, namely the range of "reference voltage .+-.0.2 to
1.0 V", preferably "reference voltage .+-.0.3 to 0.5 V" (ST-5 in
FIG. 3). If the voltage fluctuation is in the warning range, the
current is maintained according to the step ST-6 in FIG. 3, the
step ST-4 in FIG. 3 is again taken, and this step is repeated. If
the voltage fluctuation is outside the warning range, it is judged
as belonging to the "abnormality range", the current is decreased
according to the step ST-7 in FIG. 3, the step ST-3 (FIG. 3) is
again taken, and this step is repeated.
[0051] By repeating these operations, it becomes possible to
automatically operate the gas generator for generating a fluorine
or fluoride gas always safely and dependably. The above-mentioned
steps can be performed in the conventional manner, for example in
the manner of sequence control.
[0052] The present invention, which has the constitution described
above, makes it possible to automatically control the current
application to the carbon anode in gas generators for generating a
fluorine or fluoride gas by electrolysis of a hydrogen
fluoride-containing electrolytic bath. In the conventional gas
generators for industrial use, the operators are required to be
skilled and, in case of abnormality occurrence, detailed judgment
of conditions is required for modifying the operation conditions
and much cost and labor are required for stopping the gas
generators for maintenance thereof. By using the method and
apparatus for current control as invented by the present inventors,
it becomes possible to stably operate gas generators for generating
a fluorine or fluoride gas and, in case of abnormality occurrence,
it is possible to automatically cope with the abnormality and
minimize the influence of the abnormality.
* * * * *